Photoproduction of charged pions from deuterium near threshold

An experiment has been performed in order to improve existing information on the behavior of the pi-photoproduction cross section near threshold. To do this an X=ray beam from the University of Illinois betatron was passed through a 14 inch liquid deuterium bubble chamber. Each X ·-ray pulse (E max :: 230 MeV) contained a total energy of about 106 MeV. l'ne X."ray beam wa.s hardened by means of a. standard beam . hardening technique to reduce the electron background. The X-ray beam monitor was calibrated with an uncertainty of ± 2.4%. A total of 140,000 usable photographs were taken. About 5400 ." + ~ -photoproduction events and about 2700 ~ Qphotoproduction events were found. Each ~=-event was identified by a kinematic fitting of the vertex, and each n+=event was identified by a characteristic ~= ~ decay signature. Results were compared with Baldin9s impulse approximation calculations in order to obtain the matrix element for the ~=-photoproduction process from a free neutron. The results agree with the previous experiment by Adamovich et al. and with the photoproduction theory of Chew, Goldberger$ Low and Nambu. This result, however, was found to be sensitive to the so-called Ucut~offgD parameter. The .., + . ~ to ~ ratio has been dete~ned for seven pion laboratory energy and angle binsp using the ~+~events observed in deuterium. Coulomb corrections have been applied to these results. A. Chew=Low ti8unstable tar get ei extrapolation procedure was used in order to obtain the cross section for the ~=-photoproduction process from a free neutron. A. correction factor has been calculated to eliminate the effects of the Coulomb interaction and specific n~clear force interaction of the recoiling protons in the final state. The result of this analysis agrees with the CGLN theory evaluated with a coupling constant f 2= 0.·073 (=) ~ .003 and N being set to zero. The extrapolation to threshold was carried out using the cross section shape predicted by CGLN. The threshold value of BRa 0 ( .., ) Ci was found to be 26.0! 1.0 ~b/ster. Comparing th~s with the result of the latest ~ + experiment a't the University of Illinoisp the threshold t;J' -/t;+J' ratio was found to be 1.23 + .06.U of I OnlyThesi